1. Field of the Invention
This invention relates to software for the design and construction of engineering system models, and more particularly to reduction of a network topology-based system and the calibration of such a system.
2. Background Information
In many civil engineering applications, it is important to have predictive simulations for conditions for networks providing the infrastructure for a community. The simulations are used to design new portions of a civil engineering system, to rehabilitate aging sections of the civil engineering system or to perform vulnerability studies to produce risk assessments for security or other matters that may be presented which could affect the infrastructure being represented. Such simulations are performed using software that generates an engineering model of the system. An engineering model is employed for these purposes and it uses data describing field conditions, which data is assembled in a systematic manner to describe the system. For example, in a water distribution model, field conditions are assembled in a systematic manner to describe pipe flow and junction hydraulic grade lines (HGL) (which are pressures) within a water network being described by a water distribution model. The model is desirably capable of simulating conditions encountered at the site.
Models can employ a large amount of data. In many instances, all of the data is not needed to develop an understanding of the system, to perform a particular set of analyses or to produce a particular set of results for the engineering system. Thus, sometimes a portion of the data is eliminated from the model and a simpler model, involving fewer elements, is developed. This reduction process is sometimes referred to as “skeletonization” of the model. The skeletonization of a model which includes many elements develops a more compact representation of the system. There may be a target that an engineer would like to achieve, such as producing a model with 1000 pipes in a hydraulic network model, when the overall actual system includes 10,000 pipes, for example.
Several skeletonization processes have been known in the art. These processes may have conditional criteria depending upon the particular circumstances. Some topological processes involve Series Pipe and Parallel Pipe Removal whereby certain elements are combined and represented by only one pipe, for example. Branch Trimming is another method of skeletonizing a model. Another process is Data Scrubbing, in which there is a more random, blind removal of data.
Series Pipe Removal combines two pipe elements into one while the intermediate node, sometimes possessing hydraulic demand, is removed. Demand, if present on the intermediate node is reallocated in some fashion to the end nodes of the merged pipe. Demand reallocation strategies, however, typically are not comprehensive enough and limit the user to choosing from an even demand distribution or a distance weighted one. This limitation can hinder the ability to maintain an acceptable level of hydraulic parity.
Additionally, difficulty can be encountered with Series Pipe Removal in maintaining the accuracy of the representation of the system behavior in the reduced model. If the pipes to be merged have dissimilar hydraulic characteristics (roughness, diameter etc.) then the resulting pipe will not be an hydraulically equivalent representation of the original system. To combat this, current processes employ a criteria-based process, but this process can lead to fewer elements being removed during the skeletonization because the values of the potential merger candidates must usually match exactly. It would be helpful if the user could specify tolerances that determine if pipes to be merged are similar enough that combining them into a single pipe will not significantly impact the hydraulic behavior of the modeled network, as opposed to requiring values to match. Additionally, criteria and tolerances imposed on the pipe end nodes can serve as a protection against losing certain hydraulic data. For example, the user may only wish to merge two pipes if their end nodes do not vary in elevation by more than 3 feet, otherwise a loss of important pressure information may result. Up to now, the user has not usually had this level of flexibility with currently available techniques.
Parallel Pipe Removal is a process of combining pipes that share the same two end nodes. It has disadvantages similar to those of Series Pipe Removal.
Branch Trimming is another common process of removing pipes in a network for skeletonization purposes. Branch Trimming is the process of removing short, dead end links and corresponding junctions. As for Series Pipe Removal pipes and junctions (nodes) are removed by this process, thus criteria for both types of elements are specified by the user. Once again, existing tools are limited to a narrow range of criteria, usually pipe length and node elevation tolerances.
One aspect of Branch Trimming is the reallocation of demands that are associated with junctions that are removed. The demand associated with the dead end junction is assigned to the junction at the beginning of the branch. Branch Trimming is typically an effective skeletonization technique because dead end junctions with no loading have little effect on a model, and dead end junctions that do have demands are accounted for at the point through which the flow would pass without skeletonization. So, the hydraulic behavior of the network as a whole is not adversely affected. However, the disadvantage to this type of skeletonization is that information and results can not be obtained from non-existent elements, thus during water quality or fire flow analysis, information on trimmed elements may be desired, but may now be unavailable after model reduction.
The fourth type of skeletonization is that of data scrubbing. Data scrubbing is typically the simplest and generally the first step of the skeletonization process, especially for models that contain many small or insignificant elements. Some automated skeletonizers rely entirely on data scrubbing reduction techniques. Data scrubbing basically consists of simply removing all pipes that meet user-specified criteria such as diameter, roughness or other attributes. Criteria combinations can also be applied such as, “remove all two inch pipes that are less than 200 feet in length.”
The data scubbing type of skeletonization is especially useful when the model has been created in a Geographic Information System (GIS) environment. GIS maps generally contain much more information than is necessary for the hydraulic model. Examples of elements that are commonly included in GIS maps, but not necessarily in the distribution model, are service connections and isolation valves. Removing these elements generally has negligible impact on the accuracy of the model, depending upon the application for which the model is being used. The primary disadvantage of this type of skeletonization is that system integrity may not be maintained because there is typically no network awareness involved and little consideration of the hydraulic effect of the removal of an element. Thus, there is a potential for error through inadvertent pipe removal or by causing network disconnection. Most conventional skeletonization techniques do not include the ability of the user to specify that certain elements cannot be removed.
Of the four skeletonization methods discussed, each of these techniques can lose some of the information about network behavior that ideally would be included in the model. There remains a need therefore for a skeletonization tool that maintains system integrity while allowing for removal of elements according to flexible modeling criteria, while preserving the hydraulic behavior of the model.
Applying generally to the techniques of Branch Trimming, Series Pipe Removal and Parallel Pipe Removal, it is an object of the present invention to provide a method and system for skeletonization of an engineering modeling system that can employ a variety of user-specified skeletonization techniques with user-specified criteria and tolerances, while maintaining greater accuracy and predictability for the simulation of the actual engineering system being modeled.
The Data Scrubbing process, however, is unique in that it is more destructive than the other three methods and requires an alternative approach to re-introduce the hydraulics of a water distribution network model into a skeletonized model to more accurately represent system behavior. Thus, it is a further object of the present invention to provide a modeling system that maintains system integrity and allows for reduction in the number of elements in the model that achieves the goals of reducing a model for the skeletonization technique of Data Scrubbing. In addition the method used to re-instate the hydraulics after performing the data scrubbing process, can also apply to the other three skeletonization processes such that it provides a more accurate correlation between previous and new hydraulics where multiple demand conditions are present in the pre-skeletonized model.